Determine Your Energy Usage
Begin by learning how much it costs to provide your kiln with the energy (fuel or electricity) for your firings. You will want to do this calculation process for all your typical types of firings. For example, I will want to calculate for cone 08 bisque, cone 05 glaze, and cone 5 glaze firings.
Depending upon your kiln's energy source, read your electric or natural gas meter before and after each type of typical firing. Subtract the first reading from the last to give you the energy consumption during the firing. For example, if you have an electric kiln you will find out how many kilowatt hours were used during the firing.
Compute Your Energy Costs
Compute the cost per kilowatt hour (or other energy unit), using the data on your latest energy bill. If your bill does not give rates per unit, divide the total cost for the units by the number of units used over that month. For example, let's say the cost for total energy usage was $200.00 and the amount of energy used was 2500 kilowatt hours (the units). $200.00 divided by 2500 equals $0.08, or eight cents per kilowatt hour.
Now, take the amount of energy your kiln used for the firing (for the step above) and multiply it by the cost per energy unit. For example, if your kiln used up 200 kilowatt hours of energy your calculation would be 200 times $0.08 which equals an energy cost of $16.
Add in Your Overhead
For example, if you estimate that
- your kiln shelves will last 100 firings and they cost $500, then each firing cost would be $5. ($500 divided by 100.)
- If you use up one pound of dry kiln wash mixture for each glaze firing, and ten pounds of kiln wash costs $26, then the kiln wash used in each glaze firing costs $2.60.
- If it takes you an hour to stack the kiln, and a half hour to unload it, multiply your "pay rate" by 1.5. For example, if you pay yourself $7 per hour, the cost for your time would be $10.50.
Renting Kiln Space by Cubic Inches
Once you know the cost for the entire firing, it is easy to calculate how much to charge if you are renting space in your kiln (as opposed to renting the entire kiln). Take your cost for the each of your typical firing types and divide by the interior space of your kiln. For example, if your kiln has ten cubic feet of interior room, divide the total cost by ten to get the cost per foot. In our example, this would be $16 for energy plus $18 for overhead, for a total cost of $34. The $34 then is divided by 10 and equals $3.40 per cubic foot.
If you want to charge rent by the inch, since there are twelve inches in a foot, divide the cost per foot by twelve to get the cost per inch. ($3.40 divided by 12 equals just over $0.28 per inch.)